This invention relates generally to a surface hard coat for a synthetic resin lens, and more particularly to a hard coat including organic silane compounds, colloidal silica, epoxy compounds and magnesium perchlorate as a curing catalyst for providing improved abrasion resistance, hot water resistance, tintability by disperse dyes, chemicals resistance and weatherability.
A synthetic resin lens has many advantages compared to an inorganic glass lens. For example, the synthetic lens is lighter than an inorganic glass lens and provides excellent impact resistance and superior processing characteristics. On the other hand, the synthetic resin lens does have some disadvantages. Specifically, the synthetic resin lens scratches or scars easily and is affected easily by an organic solvent.
In order to overcome these disadvantages, it has been proposed to coat the synthetic resin lens with various types of hardening resins. To date, the coated synthetic resin lens has not satisfied all of the necessary requirements of a suitable lens. One such coating composition includes a combination of a hydrolyzed trifunctional silane, such as methytrialkoxysilane and a hydrolyzed tetra-functional silane, such as tetramethylsilicate and tetraethyl silicate. This coating composition has not satisfied all of the desired characteristics with respect to abrasion resistance, tintability by disperse dyes, shelf life, and the like.
It is also known that a Lewis acid or a complex thereof, Bronsted acids or metal salts of carboxylic acid can be used as a curing catalyst for an alkoxysilane including an epoxy group. However, the shelf life of such a composition containing this type of catalyst is short. Additionally, the curing takes an extended period of time. Therefore, such catalysts are not practical.
An additional coating composition for synthetic resin lenses include at least one or a mixture selected from the group of compounds including one or both of an epoxy group, silanol and/or siloxane group and fine particles of silica having a diameter between 1 to 100 millimicrons and an aluminum chelate compound as described in U.S. Pat. No. 4,211,823. Such cured coating compositions are not completely satisfactory in that sufficient hardness is not achieved and it is lowered by dipping in hot water. Additionally, the shelf life is also short.
In a synthetic resin lens, particularly one to be used for a spectacle, it is desirable that the surface coating be dyeable easily. Therefore, not only is abrasion resistance important, but also unchanged tintability over an extended shelf life is very important. Up to the present time, the following coating compositions have been utilized for this purpose. This composition includes (a) ammonium perchlorate and (b) one or more compounds selected from hydrolyzed alkoxysilanes including an epoxy group or hydrolyzed alkoxysilanes including a vinyl group, a methacryloyloxy group, amino group, a mercapto group or chlorine and (c) colloidal silica having a particle diameter of 1 to 100 .mu.m or an organic titanium compound. Another coating composition includes (a) one or more polymers or copolymers obtained by polymerization or copolymerization of an organosilicon compound including a vinyl group, a methacryloyloxy group, an amino group, a mercapto group or chlorine, hydrolyzed compounds thereof, and an epoxy compound and a vinyl monomer including at least one epoxy group in the monomeric unit; (b) a colloidal silica having a particle size diameter between 1 to 100 .mu.m; and (c) ammonium perchlorate. This latter coating composition is not entirely satisfactory in view of the limited abrasion resistance and tintability by a disperse dye. Further, the tintability by a disperse dye varies over the shelf life. Thus, these latter types of coating compositions are not entirely practical.
Accordingly, it is desirable to provide a surface hard coat for a synthetic resin lens having improved abrasion resistance, hot water resistance, stable tintability by a disperse dye, chemical resistance and weatherability which avoids the defect of the prior art compositions.